This invention relates to a marine propulsion system in which exhaust is discharged from an exhaust manifold and is mixed with water prior to discharge.
In a marine propulsion system including an internal combustion engine, it is known to mix the engine combustion product exhaust with coolant water prior to its discharge. Various structures have been developed for providing such mixing of exhaust with water. One such structure is shown in U.S. Pat. No. 4,573,318 to Entringer et al. This patent discloses an exhaust elbow for connection to a water jacketed exhaust manifold. The exhaust elbow includes an exhaust passage with a water jacket therearound. The exhaust passage communicates with an exhaust outlet provided in the engine exhaust manifold for discharging exhaust therefrom. The water jacket receives cooling water from the engine cooling system, and discharges such cooling water into the exhaust prior to discharge. This form of exhaust elbow is particularly suited for a marine propulsion system utilizing an open cooling system. Another structure for mixing engine exhaust with water prior to discharge is disclosed in copending application Ser. No. 07/177,677 filed Apr. 5, 1988 in the name of Lulloff et al, and assigned to the same assignee as is the present application. This application discloses a combination exhaust manifold and exhaust elbow, with water jackets provided around the entire assembly. This structure is also particularly suited to use with an engine which is cooled by an open cooling system. The structures disclosed in the above-noted patent documents require a machined surface for connection to the engine exhaust manifold or to the engine cylinder block, for use in conjunction with a gasket or the like to provide a seal between the surfaces. Such a gasketed connection creates the potential for leakage and/or corrosion at the gasket interface.
Additionally, the mixing of exhaust with cooling water prior to discharge can create problems with an internal combustion engine cooled by a closed cooling system. In a closed cooling system, a heat exchanger typically utilizes intake sea or lake water to cool an engine coolant, such as glycol, provided in the closed system. Thereafter, the intake water is mixed with the exhaust to cool the exhaust prior to discharge. In seawater applications, where saltwater is taken in to cool the glycol engine coolant, a corrosive reaction results when the saltwater is exposed to the exhaust gases. The spray of saltwater evaporates as it contacts the hot exhaust gases, which causes a buildup of salts on the walls of the casting. The wet, steamy environment creates galvanic corrosion, which in time will corrode through the piece in which the mixing occurs. This piece must then be replaced. With previous one-piece exhaust systems, such replacement can result in substantial expense due to the complexity of the piece.
The present invention is designed to provide a mixing tube assembly for mixing exhust gases with coolant water in an integral, one-piece tube. The tube can be a cast member with non-machined surfaces, adapted for connection to an engine exhaust manifold by means of a resilient connector member, such as a rubber boot or the like. The invention is well suited for applications involving a closed cooling system, in which the intake coolant water, such as salt water, is discharged from a heat exchanger or the like directly into an inlet provided on the mixing tube. In accordance with the invention, an integral mixing tube assembly includes an exhaust passage having an exhaust inlet for receiving exhaust from the engine and an exhaust discharge outlet downstream of the inlet. Water jacket means is provided around the exhaust passage, and includes water discharge outlet means for discharging water from the water jacket means. A water inlet is provided for introducing water into the water jacket means. In seawater applications, the water inlet introduces saltwater into the water jacket means for cooling exhaust within the exhaust passage. A mixing cavity is provided downstream of the exhaust passage and the water jacket means for receiving and mixing exhaust from the exhaust discharge outlet with water from the water discharge outlet from the water jacket means. The mixing cavity has an outlet for discharging mixed water and exhaust therefrom. As noted, the mixing tube assembly can be a cast member adapted for connection to the exhaust manifold by means of a resilient connector, such as a rubber boot. The downstream end of the mixing tube assembly can be connected by means of a resilient connector member to a discharge pipe for discharting the mixed water and exhaust. In this manner, the mixing tube assembly is essentially "suspended" from the exhaust manifold. In the event the mixing tube assembly corrodes through by the above-discussed galvanic corrosion caused by saltwater mixing with hot exhaust gases, the mixing tube assembly can simply be removed and replaced inexpensively and easily.